1. Field of the Invention
The present invention relates to a thread securing device in a sewing machine, more particularly to a thread securing device in a sewing machine wherein an upper thread located along a thread guiding path is caught during the travel of a thread take-up lever to effect automatic hooking of the thread thereto, the upper thread being secured preliminarily corresponding to the take-up amount thereof taken by the thread take-up lever so as to effectively prevent slipping off of the upper thread from the thread eye of the needle upon starting up of the sewing machine.
2. Description of the Prior Art
In sewing work fabric with a sewing machine, a thread loop to be formed in a short ascending stroke of a needle having been pierced through the fabric is adapted to be caught by the tapered hook of a shuttle in an appropriate timing. After catching of the thread loop, the upper thread has to be pulled up abruptly to release the thread loop from the tapered hook, and a thread take-up member (commonly referred to as "thread take-up lever"; the same shall be used hereinafter) is used for the above purpose. As such type of thread take-up lever, a structure is widely used wherein a link mechanism or a cylindrical cam is employed to impart a vertical arcuate orbital movement to the thread take-up lever. An operation of hooking the thread into a thread holding end of the thread take-up lever is also included in a series of operations in preparation for starting a sewing operation to extend an upper thread drawn from a spool in a predetermined order and to finally thread it into the thread eye of a needle.
The above-described thread extending operation in preparation for sewing operation using a sewing machine is generally complicated because of its complicated thread guiding path and extending order. For such reasons, various mechanisms have been proposed which can effect thread extending and threading operations automatically and are also practically utilized. The Japanese Utility Model Publication No. 43878/1979, for example, discloses a device which effects automatic threading of an upper thread into the thread eye of a needle as a suggestion made by the assignee of the present application.
There have also been suggested devices to effect automatic hooking of a thread into a thread take-up lever, for example, as in the "sewing machine" also disclosed in the Japanese Utility Model Publication No. 151681/1986 (withdrawn) filed by the assignee of the present application. In this invention, the sewing machine is constructed such that an upper thread Y, having been extended by a thread hooking member 14 during a cycle of horizontal reciprocating stroke of a thread holding end 24 of a thread take-up device in effecting thread hooking, is threaded into a thread holding hole 29 of the thread holding end 24, and under the same state, an automatic take-up of the upper thread Y is effected as the thread holding end reciprocates horizontally.
A sewing machine provided with a mechanism which effects hooking of a thread automatically into the thread holding end of the thread take-up lever as described above can be highly evaluated in that it can simplify the complicated thread hooking operation and that it has achieved an improved operability by a beginner. However, such a type of sewing machine suffers problem that a thread having been threaded into the thread eye of the needle retracts from the thread eye when the thread holding end of the thread take-up lever catches and takes up the upper thread in accordance with the movement of the thread take-up lever and to finally slip off the thread eye if the amount of thread to be taken up thereby exceeds the quantity of thread having been threaded into the thread eye and extending outward therefrom.
In such a case, an operation must be repeated to thread the upper thread into the thread eye of the needle after completion of the automatic thread hooking to the thread take-up lever, or care must be taken to pull out a sufficient amount of the upper thread manually extending out of the needle in order to prevent occurrence of the above slipping off of thread. The above operations are extremely complicated and there was hoped a device having overcome such disadvantages.